1. Field of the Invention
The present invention relates to a radiation measurement technique used in a facility for handling radioactive material, such as a nuclear power plant or the like, and more particularly, to a radiation detecting apparatus which is capable of simultaneously and independently measuring radiations such as a and xcex2 rays at a same position, and is suitable to a practical use as a radiation monitor.
2. Description of the Prior Art
FIG. 20 shows a phoswich detecting apparatus (phosphor sandwich detecting apparatus) as a conventional example of a radiation detecting apparatus for simultaneously detecting an xcex1 ray and a xcex2 ray.
This radiation detecting apparatus is provided with a light shielding film 1 through which the xcex1 and xcex2 rays are transmitted and for shielding light from the outside of the apparatus. The radiation detecting apparatus is also provided with a first scintillator 2 and a second scintillator 3 which are piled up below the light shielding film 1 shown in FIG. 26.
There are many cases where ZnS (Ag) detecting an xcex1 ray is used as the first scintillator 2, and plastic detecting xcex1 and xcex2 rays is used as the second scintillator 3. The first and second scintillators 2 and 3 piled into two layers are directly mounted to a photo detector 5 so as to be received in a case 6. In general, a photo-multiplier tube having a high speed response and a high sensitivity is used as the photo-detector 5.
A decay time constant of emission of ZnS (Ag) constituting the first scintillator 2 is xcexc sec order, but that of emission of plastic constituting the second scintillator 3 is several tens of n sec order. Therefore, the decay time constant of emission of the plastic scintillator 3 is considerably shorter as compared with that emission of the ZnS (Ag) first scintillator 2. When an output current signal of the photo-detector 5 is converted into a voltage signal by means of an RC integrating circuit having a sufficiently long time constant as compared with each decay time constant of emission of the scintillators 2 and 3, a pulse rise time is substantially equal to a decay time of emission, and shows an index decay waveform of a time constant determined by a resistor R and a capacity C. This signal converting process can be carried out in a pre-amplifier unit connected to the photo-multiplier tube and included in the photo-detector 5.
The converted voltage signal is amplified up to a voltage level which is capable of being analyzed by means of a waveform discrimination processing unit 7, as the necessity arises. When the voltage signal is inputted in the waveform discrimination processing unit 7, an analog-digital converter of the processing unit 7, in order to output a pulse signal having a pulse height proportional to the rise time of the inputted signal, converts the pulse height of the inputted signal into a digital value so that a general analyzer of the processing unit 7 measures a pulse height distribution (a spectrum data) on the basis of the converted digital value.
It is possible to distinguish an emission of the first scintillator 2 and that of the second scintillator 3 on the basis of the spectrum data showing the rise time and obtained from the waveform discrimination processing unit 7.
FIG. 21 shows, as another conventional example, an xcex1-xcex2 rays detecting apparatus using a sensor 8 for measuring energy spectrum.
For example, an Si semiconductor sensor is used as the sensor 8 for measuring energy spectrum of the above apparatus. However, the sensor 8 has a sensitivity to a room light and the like other than a radiation; for this reason, similarly to the above described radiation detecting apparatus, a light shielding film 1 is mounted on the sensor 8 so that the sensor 8 is housed in a case 6.
An output signal of the sensor 8 is analyzed by means of a pulse height analysis system 9, so as to be measured as an energy spectrum. In general, the analysis system 9 includes: a charge sensitive pre-amplifier for processing the sensor output signal; a linear amplifier, an analog-digital converter, a pulse height analyzer for analyzing multiple pulse heights and the like. In the energy spectrum data obtained by the analysis system 9, the xcex1-ray data and the xcex2-ray data show different distributions and peak shapes, respectively, and therefore, it is possible to distinguish the xcex1 ray and the xcex2 ray by processing these spectrum data corresponding to the a and xcex2 rays.
However, the pulse height discrimination processing unit 7 necessary for the conventional phoswich detecting apparatus shown in FIG. 20 is a processing unit for analyzing a pulse rise, and is very expensive. Therefore, this conventional detecting apparatus is useful to a study in an experimental level.
However, as a detecting apparatus which is mounted in a monitoring device used in an actual nuclear facility or the like, there is a problem relating to a cost. Moreover, the waveform discrimination processing unit analyzes a rise time itself, and is an over specification in the case of discriminating signals having different rise times, respectively.
Furthermore, in view of the principle, in order to obtain a rise time, for example, there is a need of carrying out a signal detection at a 10% level and a 90% level of an inputted pulse height value, so that there is a problem that it is impossible to analyze and measure a signal having a low pulse height value. This problem relates to a dynamic range of the pulse height value of the signal. For example, an emission of ZnS (Ag) scintillator generated by an xcex1 ray is considerably larger than that of the plastic scintillator generated by a xcex2 ray, and actually, the output signal of the photo-multiplier tube corresponding to the emission of ZnS (Ag) is larger 10 times or more as much as that of the photo-multiplier tube corresponding to the emission of xcex2 ray of the plastic scintillator at the point of time of being converted into the voltage signals.
Therefore, since the xcex2 ray signal has a low pulse height value and is continuously distributed on a low energy side, the measurement of the xcex2 ray is disadvantageous as compared with that of the xcex1 ray. In particular, a component of the xcex2 ray having a low pulse height value is not analyzed and measured so that there is a problem that an effective xcex2-ray sensitivity gets to be low. Especially, in the case where a thickness of the plastic scintillator is made thin in order to suppress a xcex3-ray sensitivity, the emission of the plastic scintillator is further lowered so that the aforesaid phenomenon of lowering the effective xcex2-ray sensitivity is further accelerated.
In addition, in the case of the radiation detecting apparatus using the energy spectrum measuring sensor 8 as shown in FIG. 21, the pulse height analyzer which is substantially equal to the above waveform discrimination processing unit must be required; as a result, there is a problem that the cost of the radiation detecting apparatus gets to be high. Furthermore, since an effective atomic weight of a base material of the energy spectrum measuring sensor 8 is larger than the plastic scintillator, a xcex3-ray sensitivity is high so that there is a problem that a xcex3-ray signal is mixed into a xcex2-ray signal.
Still furthermore, in the case where measurement is not carried out in a vacuum state, or in the case of measuring an xcex1 ray from an xcex1-ray emission nuclide absorbed to a filter paper, an energy loss of the xcex1-ray is high and a fluctuation of range is large. For this reason, a Gaussian peak as obtained in vacuum is not obtained so that there is the case where the energy spectrum of the xcex1-ray overlaps with that of the xcex2-ray, whereby, in spite of measuring the energy spectrums of the xcex1 and xcex2 rays, it is hard to clearly distinguish the xcex1 ray and the xcex2 ray.
The present invention is directed to overcome the foregoing problems.
Accordingly, it is an object of the present invention to provide a radiation detecting apparatus which is capable of practically being used as a detector for radiation monitor, and being manufactured at a low cost, and further is able to independently and simultaneously detect an xcex1 ray and a xcex2 ray while maintaining sensitivities of these rays at the utmost limit and sufficiently preventing a xcex3 ray sensitivity.
In addition, it is another object of the present invention to provide a radiation detecting apparatus having a rationally arrangement of first and second photo-detectors so as to make high an efficiency of detecting emissions of the first and second scintillators.
That is, in the radiation detecting apparatus, as described above, a light emitted in the first scintillator for xcex1 ray transmits through the second scintillator for xcex2 ray, and then, is guided to at least one photo-detector by means of condensing means. In this case, conventionally, the waveform discrimination processing unit for analyzing a rise of pulse has been applied in view of a pulse rise time of a signal converted by an RC integrating circuit, wherein the pulse rise time is substantially equal to a decay time of emission of each scintillator.
In view of this point of using the waveform discrimination processing unit, the inventors have a concept that it is possible to dispense with the waveform discrimination processing unit for analyzing a pulse rise, which is required for the conventional radiation detecting apparatus, by adjusting and optimizing the used scintillators, emission wavelengths of the scintillators and quantities of emission thereof.
More specifically, it is preferable that a photo-multiplier tube is used as a photo-detector in view of a response speed and sensitivity.
In other words, since the emission wavelength of the first scintillator is set to be different from that of the second scintillator, it is possible to adjust and optimize the scintillators, emission wavelengths of these scintillators and quantities of emission thereof in accordance with those. Furthermore, a detecting apparatus is constituted by intentionally varying the emission decay times of these scintillators and emission wavelengths thereof, whereby it is possible to provide means for optically discriminating between the emission wavelengths of these scintillators.
Moreover, as means for independently and simultaneously detecting an xcex1 ray and a xcex2 ray while securing the maximum sensitivity of them, the inventors have a concept that a light is easy to be confined in the first and second scintillators so as to improve each condensing density of each of the first and second scintillators by an arrangement thereof. More specifically, the first scintillator emitting a light by an xcex1 ray is formed very thin so as to restrict xcex2-ray and xcex3-ray sensitivities, and for example, there are many cases where the first scintillator is composed of a powder, a sintering body and other similar materials. Therefore, in the first scintillator, a diffuse reflection is made therein so that a light is emitted thereto. The emitted light transmits through the second scintillator for a xcex2 ray so as to be guided to the photo-detector by the condensing means.
In this structure, in the case where an air is interposed between the first and second scintillators, when the light emitted from the first scintillator is transmitted through the second scintillator, though a probability of an occurrence of Fresnel reflection increases, since the second scintillator is surrounded by the air having a refractive index value lower than that of the second scintillator, it is easy to confirm the light emitted in the second scintillator. For this reason, as the condensing means for the second scintillator, it is easy to employ a method of using the emitted light condensed on the edge side of the second scintillator with a high density.
In accordance with the above described conception, in order to achieve such objects, according to one aspect of the present invention, there is provided a radiation detecting apparatus comprising: a light shielding film for transmitting therethrough first and second radiations while shielding an incidence of light; a first scintillator for emitting a first light by the first radiation transmitted through the light shielding film, the first scintillator having an emission center wavelength based on the first radiation; a second scintillator for emitting a second light by the second radiation transmitted through the light shielding film, the second scintillator having an emission center wavelength based on the second radiation; and detection means having at least one photo-detector for detecting the first light emitted from the first scintillator and the second light emitted in the second scintillator, the first emission center wavelength and the second emission center wavelength being different from each other.
In preferred embodiment of this one aspect, the first emission center wavelength is a wavelength of the first light emitted in the first scintillator and having a peak emission intensity in an emission wavelength band of the first scintillator, and the second emission center wavelength is a wavelength of the second light emitted in the second scintillator and having a peak emission intensity in an emission wavelength band of the second scintillator.
In preferred embodiment of this one aspect, the first scintillator and second scintillator are arranged in parallel to each other so that the second scintillator is located away from the first scintillator at a predetermined distance, further comprising means for condensing the first light emitted from the first scintillator and the second light emitted in the second scintillator on the detection means; and an air layer interposed between the first and second scintillators, the first emission center wavelength of the first scintillator being set shorter than the second emission center wavelength of the second scintillator.
According to the one aspect of the present invention described above, the air layer is interposed between the first and second scintillators, and thereby, the second scintillator is surrounded by the air layer having a refractive index value lower than itself, so that the second light is confined in the second scintillator. Therefore, it is easy to employ a method of using a light condensed on the edge side of the second scintillator with a high density. Furthermore, there is no need of providing an intermediate material required for bonding of these first and second scintillators and optically closely connecting them. In addition, the present invention is suitable for the case where there is an anxiety of alteration due to a chemical interaction of these intermediate materials and the first and second scintillators. Still furthermore, an independence of each scintillator is secured, making it possible to carry out maintenance, inspection and replacement with respect to only one of these scintillators.
Moreover, the emission center wavelength of the first scintillator is set shorter than the emission center wavelength of the second scintillator, making it possible to also use means for optically identifying wavelengths of the first and second lights so as to dispense a waveform discrimination processing unit for analyzing pulse rise times.
This one aspect of the present invention further has means for condensing the first light emitted from the first scintillator and the second light emitted in the second scintillator on the detection means, wherein the first scintillator and second scintillator are closely optically adhered with each other, the first emission center wavelength of the first scintillator being set shorter than the second emission center wavelength of the second scintillator.
According to the one aspect of the present invention, the first and second scintillators are arranged so as to optically closely be adhered with each other, making it possible to reduce an internal capture by a Fresnel reflection based on a difference in refractive indexes due to the air layer and by a total internal reflection in the second scintillator, and thus improving a transmission probability of the first light of the first scintillator through the second scintillator. Therefore, it is easy to employ of using the second light from the back surface of the second scintillator which is not adhered with the first scintillator.
This one aspect of the present invention further has means for condensing the first light emitted from the first scintillator and the second light emitted in the second scintillator on the detection means, wherein the first scintillator and second scintillator are closely optically adhered with each other, the first emission center wavelength of the first scintillator being set longer than the second emission center wavelength of the second scintillator.
According to the one aspect of the present invention, the first and second scintillators are arranged so as to optically and closely be adhered with each other, making it possible to improve a transmission probability of the first light of the first scintillator through the second scintillator. Therefore, it is easy to employ a method of condensing the first light of the first scintillator from the back surface of the second scintillator, as the condensing means.
One aspect of the present invention further has a condensing box for condensing the first and second lights on the detection means, the condensing box having an inner surface for diffusely reflecting the first and second lights and a side surface, the light shielding film being mounted on the side surface on which the first and second radiations incident, the first and second scintillators being arranged inside the light shielding film, and wherein the detection means comprises first and second photo-detectors each having a sensitive surface sensitive to each of the first and second lights; a first filter mounted on the sensitive surface of the first photo-detector; and a second filter mounted on the sensitive surface of the second photo-detector, the first filter being adapted to transmit therethrough only the first light emitted from the first scintillator, the second filter being adapted to transmit therethrough only the second light emitted in the second scintillator.
In the case of the one aspect of the present invention, the first and second lights having different emission wavelength bands are mixed to be filled in the condensing box while diffusely being reflected. The first filter is mounted on the sensitive surface of the first photo-detector, and the second filter is mounted on the sensitive surface of the second photo-detector. Because the first filter is adapted to transmit therethrough only the first light emitted from the first scintillator, and the second filter is adapted to transmit therethrough only the second light emitted in the second scintillator, it is possible to independently detect the first and second lights corresponding to the first and second radiations without using a specific electronic equipment for discrimination and identification. Furthermore, the condensing box is used so that it is easy to apply a large-area scintillator to the radiation detecting apparatus.
In preferred embodiment of this one aspect, the second scintillator has an incident surface on which the first and second radiations are incident and a back surface opposite to the incident surface, the detection means comprises first and second photo-detectors each having a sensitive surface sensitive to each of the first and second lights; a first filter mounted on the sensitive surface of the first photo-detector; and a second filter mounted on the sensitive surface of the second photo-detector, the first filter being adapted to transmit therethrough only the first light emitted from the first scintillator, the second filter being adapted to transmit therethrough only the second light emitted in the second scintillator, and wherein the first filter and the second filter are closely optically adhered on the back surface of the second scintillator.
In preferred embodiment of this one aspect, the second scintillator has a substantially rectangular shape, and wherein the first photo-detector and the second photo-detector are adjacently arranged so that a line is crossed to a longitudinal direction of the second scintillator, the line connecting a center point of the sensitive surface of the first photo-detector and that of the sensitive surface of the second photo-detector.
According to the one aspect of the present invention, it is possible to extremely decrease a probability that, when the second light emitted in the second scintillator away from the second filter is propagated therein, the second light passes on the first filter so as to be absorbed therein.
In preferred embodiment of this one aspect, the second scintillator has a substantially rectangular shape, and wherein the first photo-detector and the second photo-detector are arranged on both lateral sides of the second scintillator so that the first photo-detector is the most distant from the second photo-detector.
According to the one aspect of the present invention, it is possible to extremely decrease a probability that, when the second light emitted in the second scintillator away from the second filter is propagated therein, the second light passes on the first filter so as to be absorbed therein.
This one aspect of the present invention has an arrangement that the second scintillator has an incident surface on which the first and second radiations are incident and a back surface opposite to the incident surface, the detection means comprises first and second photo-detectors each having a sensitive surface sensitive to each of the first and second lights; a first filter mounted on the sensitive surface of the first photo-detector; and a second filter mounted on the sensitive surface of the second photo-detector, the first filter being adapted to transmit therethrough only the first light emitted from the first scintillator, the second filter being adapted to transmit therethrough only the second light emitted in the second scintillator, and wherein the first filter is arranged to be away from the back surface of the second scintillator at a predetermined interval so that an air layer is interposed between the back surface of the second scintillator and the first filter, and the second filter is closely optically adhered on the back surface of the second scintillator.
According to the one aspect of the present invention, it is possible to, when the second light emitted in the second scintillator away from the second filter is propagated therein, prevent the second light from passing on the first filter so as to get rid of the absorbing function of the second light by the first filter.
In preferred embodiment of this one aspect, the second scintillator has an incident surface on which the first and second radiations are incident and a back surface opposite to the incident surface, the detection means comprises first and second photo-detectors each having a sensitive surface sensitive to each of the first and second lights; a first filter mounted on the sensitive surface of the first photo-detector; and a second filter mounted on the sensitive surface of the second photo-detector, the first filter being adapted to transmit therethrough only the first light emitted from the first scintillator, the second filter being adapted to transmit therethrough only the second light emitted in the second scintillator, and wherein the first filter is arranged to be away from the back surface of the second scintillator at a predetermined interval, and the second filter is closely optically adhered on the back surface of the second scintillator, further comprising a surrounding box having an inner surface portion for surrounding a back surface side of the second scintillator so as to form a closed space therein, the back surface of the second scintillator and the first filter forming parts of the inner surface portion of the surrounding box, the inner surface portion of the surrounding box except for the back surface of the second scintillator and the first filter being processed to totally internally reflect diffusely the first light emitted from the first scintillator.
According to the one aspect of the present invention, it is possible to get rid of a bad influence of the first filter with respect to the second light incident through the second filter into the second photo-detector and to increase a probability that the first light emitted from the first scintillator and transmitted through the second scintillator is diffusely reflected to be detected through the first filter by the first photo-detector.
In preferred embodiment of this one aspect, the inner surface portion comprises a plurality of inner surfaces, each of the inner surfaces is inclined so that the diffusely reflecting directions on average of the first light on the inner surfaces of the surrounding box are substantially directed to a position of the second scintillator at which a center axis of the sensitive surface of the first photo-detector is crossed.
According to the one aspect of the present invention, it is possible to get rid of a bad influence of the first filter with respect to the second light incident through the second filter into the second photo-detector, and to reflect on average the first light emitted from the first scintillator and transmitted through the second scintillator toward a position of the second scintillator at which a center axis of the sensitive surface (first filter) of the first photo-detector is crossed, thereby increasing the probability that the first light is detected by the first photo-detector as compared with the first light which is uniformly distributed in the closed space.
This one aspect of the present invention further has a light guide in which the first light emitted from the first scintillator and the second light emitted in the second scintillator are incident, the light guide being adapted to condense the first and second lights on the detection means, and wherein the detection means comprises first and second photo-detectors each having a sensitive surface sensitive to each of the first and second lights; a first filter mounted on the sensitive surface of the first photo-detector; and a second filter mounted on the sensitive surface of the second photo-detector, the first filter being adapted to transmit therethrough only the first light emitted from the first scintillator, the second filter being adapted to transmit therethrough only the second light emitted in the second scintillator.
According to the one aspect of the present invention, the first and second lights having different wavelength bands are filled to be diffused in the light guide in a state of being mixed, and then, is propagated to the first and second photo-detectors. The first filter is mounted on the sensitive surface of the first photo-detector and the second filter is mounted on the sensitive surface of the second photo-detector. Because the first filter is adapted to transmit therethrough only the first light emitted from the first scintillator and the second filter is adapted to transmit therethrough only the second light emitted in the second scintillator, it is possible to independently detect the first and second lights corresponding to the first and second radiations without using a specific electronic equipment for discrimination and identification.
In preferred embodiment of this one aspect, the first filter is arranged to be away from the back surface of the second scintillator at a predetermined interval, and the second filter is closely optically adhered on the back surface of the second scintillator, and wherein the light guide has an opening surface opposite to the back surface of the second scintillator, the light guide being arranged so that the opening surface thereof being away from the back surface of the second scintillator at a predetermined interval so as to interpose an air layer between the opening surface of the light guide and the back surface of the second scintillator, the opening surface thereof having an area which is larger than that of the first filter.
According to the one aspect of the present invention, it is possible to get rid of a bad influence of the first filter with respect to the second light incident through the second filter into the second photo-detector. Moreover, since the first light emitted from the first scintillator and transmitted through the second scintillator is incident in the light guide so as to be guided through the first filter into the first photo-detector, it is possible to increase a probability that the first light is detected by the first photo-detector.
This one aspect of the present invention further has a light guide connecting the at least one photo-detector to an edge portion of the second scintillator, the light guide being adapted to convert the second light to a fluorescent light.
In the case of the one aspect of the present invention, an air is interposed between the first and second scintillators. Since the first scintillator is composed of, for example, a powder and a sintering substance or the like, a diffuse reflection is made in the first scintillator so that the diffusely reflected first light is emitted outside, thereby being once transmitted through the second scintillator, and thereafter, is filled in the condensing box. The first light filled in the condensing box is detected by means of, for example, a first photo-detector arranged in the condensing box. A component of the second light from the second scintillator is incident upon the condensing box; however, the second light is eliminated by, a filter provided on the first photo-detector.
The second scintillator is surrounded by an air; for this reason, the second light is confined in the second scintillator by a total internal reflection effect. As a result, a scintillation light is condensed on the edge portion of the second scintillator with a high density. The second scintillator is provided at the edge portion side of the second scintillator with the light guide containing a fluorescent substance of absorbing a scintillation photon and emitting a fluorescent light having a longer wavelength as compared with the second light, and thereby, a re-emission light occurs by a fluorescence conversion in the second scintillator. Since the re-emitted light is propagated while being totally internally reflected in the light guide, it is possible to detect a fluorescence light induced by re-emitted scintillation light by means of the photo-detector arranged on the end side of the light guide. Incidentally, the light guide may includes an optical fiber having a clad (referred to a fluorescence fiber, a wavelength shift fiber or the like).
In the condensing system on the edge side of the second scintillator, it is possible to condense the second light without depending upon an area of the second scintillator; and therefore, it is easy to apply the invention to a large-area scintillator together with the condensing box.
In preferred embodiment of this one aspect, the second scintillator has an incident surface on which the first and second radiations are incident and a back surface opposite to the incident surface, further comprising a fluorescent screen arranged on a back surface side of the second scintillator and opposite through an air layer to the back surface thereof, the fluorescent screen being adapted to convert the first light emitted from the first scintillator to a fluorescent light; and a light guide adapted to condense the converted fluorescent light on the at least one photo-detector, the converted fluorescent light being emitted from a surface of the fluorescent screen, the at least one photo-detector detecting the condensed fluorescent light.
According to the one aspect of the present invention, the first light from the first scintillator is transmitted through the second scintillator so as to be absorbed in the fluorescent screen, so that a re-emission of the fluorescence having a longer wavelength as compared with the second light is generated in the fluorescent screen. The re-emitted light is guided to the photo-detector via the light guide. Whereby it is possible to detect the fluorescence light induced by the first light.
In preferred embodiment of this one aspect, the second scintillator has an incident surface on which the first and second radiations are incident and a back surface opposite to the incident surface, further comprising a fluorescent screen arranged on a back surface side of the second scintillator and opposite through an air layer to the back surface thereof, the fluorescent screen being adapted to convert the first light emitted from the first scintillator to a fluorescent light; and a second light guide having a fluorescent substance adapted to absorb the converted fluorescent light so as to emit a fluorescent light, the converted fluorescent light by the fluorescent screen being emitted from an edge portion of the fluorescent screen, the fluorescent light emitted from the light guide having a wavelength which is longer than that of the converted fluorescent light by the fluorescent screen, the at least one photo-detector detecting the fluorescent light emitted from the second light guide.
According to the one aspect of the present invention, the first light from the first scintillator is transmitted through the second scintillator so as to be absorbed in the fluorescent screen so that a re-emission of the fluorescence having a longer wavelength is generated in the fluorescent screen. In this case, since the fluorescent screen is surrounded by an air, the first light is captured by the total internal reflection similarly to the second scintillator, and then, a fluorescence light is collected on the edge portion side of the fluorescent screen with a high density. Furthermore, since the fluorescent screen is provided with the second light guide for absorbing the fluorescent light generated in the fluorescent screen so as to emit a fluorescence light having a longer wavelength as compared with the fluorescent light generated in the florescence screen, it is possible to condense the emitted fluorescent light by a fluorescence conversion from the edge portion side of the fluorescent screen similarly to the second scintillator. Since the second light guide is provided at the edge portion of the second light guide with the photo-detector, it is possible to detect the first light of the first scintillator as a light which is double converted into a fluorescent light.
The one aspect of the present invention further has means for capturing a signal outputted from the detection means so as to recognize a signal having a predetermined pulse height value and over as an optical signal thereby eliminating a signal less than the predetermined pulse height value as a noise, the optical signal corresponding to at least one of the first and second lights emitted from the first and second scintillators.
According to the one aspect of the present invention, a signal outputted from the detection means is captured so that a signal having a predetermined pulse height value and over is recognized as an optical signal. On the other hand, a signal less than the predetermined pulse height value is eliminated as a noise.
In preferred embodiment of this one aspect, the detection means comprises a plurality of photo-detectors, a first group of the photo-detectors being adapted to detect the first light emitted from the first scintillator, a second group thereof being adapted to detect the second light emitted from the second scintillators, further comprising means for capturing signals outputted each of the first and second groups of the photo-detectors and, in a case of detecting signals outputted from at least one of the first and second groups of the photo-detectors, for recognizing detected signals corresponding to at least one of the first and second lights emitted from the first and second scintillators and, in a case where only one signal is outputted from at least one of the first and second groups of the photo-detectors, for eliminating the only one signal as a noise.
According to the one aspect of the present invention, the first lights are detected by the first group of the photo-detectors and the second lights are detected by the second group thereof. Each signal of each of the first and second groups of the photo-detectors is captured by the capturing means so that, in the case where signals outputted from at least one of the first and second groups of the photo-detectors are detected, it is recognized that the detected signals correspond to the first and second lights emitted from the first and second scintillators and, in a case where only one signal is outputted from at least one of the first and second groups of the photo-detectors, the signal is eliminated as a noise.
This one aspect of the present invention further has an optical attenuation filter for transmitting therethrough the first and second radiations and attenuating an intensity of the first light emitted from the first scintillator, the optical attenuation filter being interposed between the first and second scintillators; a condensing box for condensing the first and second lights on the detection means, the condensing box having an inner surface for diffusely reflecting the first and second lights; and means for inputting signals detected by the detection means so as to discriminate, according to a difference of waveforms of the inputted signals, between an optical signal corresponding to the first light emitted from the first scintillator and an optical signal corresponding to the second light emitted from the second scintillator.
The one aspect of the present invention further has an optical attenuation filter for transmitting therethrough the first and second radiations and attenuating an intensity of the first light emitted from the first scintillator, the optical attenuation filter being interposed between the first and second scintillators; a light guide in which the first light emitted from the first scintillator and the second light emitted in the second scintillator are incident, the light guide being adapted to condense the first and second lights on the detection means; and means for inputting signals outputted from the detection means so as to discriminate, according to a difference of waveforms of the inputted signals, between an optical signal corresponding to the first light emitted from the first scintillator and an optical signal corresponding to the second light emitted from the second scintillator.
In accordance with the one aspect of the present invention, the first and second radiations are transmitted through the optical attenuation so that the intensity of the first light is attenuated. The signals detected by the detection means are inputted to the discriminating means so that the detected signals are discriminated, according to a difference of waveforms of the inputted signals, between the optical signal corresponding to the first light emitted from the first scintillator and the optical signal corresponding to the second light emitted from the second scintillator.